Feed and tension mechanisms for wire strapping machine commonly have two wheels of differing size each having a smooth surfaced peripheral groove for contact with opposite sides of the wire. Generally, the smaller wheel is driven and the larger wheel is geared to the smaller one by external teeth on the wheels. The larger wheel is usually mounted on an eccentrically located bearing shaft displaced from the axis of the wheel in the lower 90.degree. quadrant on the entry side of the wheel with respect to the direction in which the wire is tensioned just before tying, i.e. the reverse direction opposite from that in which the wire is fed into a loop track around the article. A spring pressed lever attached to the hub of the large wheel biases the larger wheel toward the smaller wheel so as to create a force moment about the eccentric axis of the large wheel. In this design, in order to obtain sufficient friction for tensioning, it is required that the wire be guided along a full 90.degree. quadrant of the groove in the outer periphery of the large wheel. This requirement limits the available locations at which the feed and tension mechanism can be placed in equipment of this design. Examples of such mechanisms are shown in U.S. Pat. Nos. 3,447,448; 3,295,436; 3,274,921; and 3,884,139. On the other hand, a feed and tension mechanism for flat strapping which does not require guiding the strap around a 90.degree. quadrant of the feed wheel is shown in U.S. Pat. No. 3,272,113. In this latter patent, two wheels of the same diameter are provided, one of which is eccentrically mounted in an upper portion of the lower 90.degree. quadrant on an exit side of the wheel with respect to the direction of tensioning. A spring pressed lever attached to the hub of the eccentrically mounted wheel biases this wheel toward the other wheel creating a force moment about the eccentric axis thereof. In this reference, only the eccentrically mounted wheel is driven which is accomplished by a complex set of gears located internally within the driven wheel. Both wheels have peripheral teeth for digging into the surface of the flat strapping in order to obtain sufficient friction for tensioning. Such wheels cannot be used on wire material because the teeth dig into the surface creating defects which are destructive to the twist knots made to secure the wire around the article. The twist knots made in the wire are distinguishable from the sealed or punched fastenings made in flat strapping materials where scratch-type defects are not harmful.
It is therefore a primary object of this invention to provide a feed and tension mechanism for wire strapping machines which does not require guiding the wire over a 90.degree. quadrant of a feed and tension wheel and in which the feed and tension wheels have smooth surface peripheral grooves so as not to damage the wire.